The present invention is directed to fluidized bed reactors, particularly multi-stage or multi-bed fluidized bed reactors and processes utilizing such reactors for coating particulate materials.
Single stage (or bed) fluidized reactors are well known and have been extensively developed. See for example, Sigai, U.S. Pat. No. 4,585,673, the disclosure of which is hereby incorporated herein by reference. See also, Kunii et al., "Fluidization Engineering" R. E. Krieger Publishing Co., Huntington, N.Y. (1977), particularly pp. 489-493. Multi-stage fluidized bed reactors are also known, but not as extensively developed as the single stage variety.
In Hemminger, U.S. Pat. No. 2,494,337 there is described an apparatus for contacting finely divided solid particles with gaseous material which comprises vertically positioned fluid beds with downcomers. While the phrase "multi-stage fluid bed reactor" is not used anywhere in the patent, the apparatus is a multi-stage unit.
In Schlamersdorf, U.S. Pat. No. 3,886,895, there is described an apparatus for treating particulate matter while in a fluidized state. This patent does not deal with multi-stage fluid beds. It concerns a plurality of single fluidized beds, "each of which operates in a substantially independent manner". In a multi-stage fluid bed, each stage is fed with powder from the stage prior to it and does not operate independent of each other.
The present invention provides advantages heretofore unavailable in previously available single and/or multi-stage fluidized bed reactors.